47.55472, -94.093701
Overview
The purpose of this study is to demonstrate different retention patterns of red pine as stands approach old age. This study will demonstrate and test differing spatial patterns and densities in old age red pine stands as a means to promote multi-cohort, structurally and biologically complex stands that will produce both silvicultural and economic outcomes. Silvicultural and economic management outcomes include; quality production, quantity production, production of specific materials and sound ecological management for all products. This demonstration is unique because it has not been implemented at this age of stand in the lakes states region to our knowledge.
The stand will be commercially thinned to a residual stand average of 60 sq ft per acre using differing levels of retention distributed across the 15 acres. The demonstration area will contain three 1/2-acre aggregates of unthinned forest, three 1/4-acre aggregates of unthinned forest, and the remainder of the stand will be thinned to a residual basal area of 37.5 sq ft per acre. No new roads or landings would be needed as this stand is bordered by forest road 2171 and access points are already established from adjoining units.
The short-term goals are to increase species and structural diversity, and to create variation in canopy cover, tree density, and understory plant community development. The long-term goals are to increase stand heterogeneity and achieve structure associated with multi-cohort red pine stands, increase species diversity and stand structure, increase and maintain dead woody debris, minimize windthrow, increase growth of residuals, and retain large individuals.
Figure 1: CNF variable retention red pine treatment aerial image.
Silviculture Objective(s)
The prescription called for a commercial thin between December 1, 2010 and May 15, 2011.
Short-term: Thin to a stand-level average of 60 ft2/ac residual basal area using variable retention of unthinned reserve patches embedded within a thinned forest.
The stand will remain a red pine community with short-term goals of increasing species and structural diversity. This intermediate entry would provide improved growing conditions for dispersed residual trees while maintaining species and structural diversity for wildlife objectives within aggregate reserves. Create variation in canopy cover, tree density, and understory plant community development. Red pine would continue to be the primary overstory species, but other species components would be present (e.g. white pine, white spruce, paper birch) in higher percentages than pre-harvest conditions.
Long-term (including future entry needs): Increase stand heterogeneity and achieve structure associated with multi-cohort red pine stands. Goals include: increasing species diversity and stand structure; increase and maintain dead woody debris, minimize windthrow, increase growth of residuals, and retain large individuals.
Pre-treatment stand description and condition
Pre-treatment species composition:
This stand is dominated by red pine in the overstory. Scattered overstory components include white pine, paper birch, balsam fir, and white spruce. Red maple, paper birch, white pine and white spruce seedlings and saplings are scattered in the understory.
Figure 2: A photo of the composition of the stand pre-harvest.
Pre-treatment forest health issues:
Deer browse is a concern for regeneration. Some existing armillaria root rot pockets are present in the stand.
Landowner objectives/situation:
This prescription is being conducted as an experiment to demonstrate different retention patterns of red pine as stands approach old age, and it will demonstrate and test differing spatial patterns and densities in old age red pine stands as a means to promote multi-cohort, structurally and biologically complex stands and will produce both silvicultural and economic outcomes.
Silviculture Prescription
Harvest Method: Commercial thin
Season of Operation: Winter harvest between December 1, 2010 and May 15, 2011;
Marking Guide and Mitigations:
- Use a variable retention approach to thin stand to an average of 60 ft2/ac residual stand basal area. This prescriptions variable retention approach consists of unthinned reserve patches of two sizes (¼- and ½-acre) and a thinned matrix.
- Unthinned reserve patches: Leave 15% of the stand in three ¼-acre and three ½-acre reserves patches to provide natural tree mortality and for wildlife objectives.
- Reserve patches are uncut “Skips” that are identified by unique attributes to be reserved.
- Large snags, unique species, structurally unique, large downed dead wood, unique understory species, or advanced regeneration.
- Create circular patches with 59 and 83 foot radius, respectively, for ¼- and ½-acre reserve patches.
- Reserve patches are uncut “Skips” that are identified by unique attributes to be reserved.
- Thinned matrix: Between the reserve patches, thin to 37.5 ft2/ac residual stand basal area by dispersed free thinning to maximize species diversity and structural complexity.
- Mark reserve trees that are windfirm and in dominant canopy positions.
- Maximize species diversity in reserve trees.
- Thin primarily from below.
- Cut primarily suppressed or codominant red pine and jack pine to maintain existing species diversity in the stand. Retain other species unless needed for operability.
- Leave at least 6-10 standing dead, suppressed, or dying conifers per acre. Preference is given to short-lived species, such as jack pine. Other species include white spruce, balsam fir, red and white pine, black spruce and tamarack. Trees may be scattered or clumped. Snags greater than 12 inches will be marked as reserve. Retain dying, damaged, and diseased pine for wildlife (e.g., black-backed woodpecker). Retain existing snags greater than 5 inches unless a safety hazard.
- Protect conifer regeneration as possible throughout the site.
- Lop and scatter slash within 3’ of ground throughout stand.
- Goshawk nest post-fledging area: maintain an average of 70 percent canopy cover across the 250 acre post-fledging area.
Figure 3: Variable retention harvest
Post-harvest Treatment:
Site Preparation: Implement mechanical reduction of shrub and slash after harvest on the thinned portion of the stand with the use of Chippewa harrow (disc's mounted on a skidder).
Figure 4: The structure of the stand upon completion of disking.
Reforestation: Planting additional species after harvest and site preparation; planting would be conducted in the thinned portion of the stand at a density of 200 trees per acre each of white pine, jack pine, and white spruce.
Stand Protection: Bud capping as necessary to protect planted seedlings from deer browse annually for up to 5 years
Individual Tree Release: If necessary, release planted stock at year 4 post-planting to promote growth and survival of planted seedlings.
Post-treatment assessment
The average stems per acre five years after the treatment can be seen in Table 1. Figure 2 below further breaks down the stems per acre by species and site prep treatment for the pre-harvesting conditions as well as the post-harvesting conditions up to five years after the treatment.
Table 1. Average stems per acre five years post-treatment.
| PIGL | PIRE/PIBA | PIST | QURU | ACRU | ABBA | HAZEL | RASPBERRY |
| 90 | 135 | 562 | 517 | 4811 | 472 | 33477 | 14299 |
Figure 5: The stems per acre broken down by species and site prep treatment for the pre-harvesting conditions as well as the post-harvesting conditions up to five years after the treatment.
The Northern Research Station monitored planted stock survival on 30 seedlings of each species over five years following treatment. Table 2 shows survival of the three planted species based on planting location in a harrowed area vs. a non-harrowed area. Figure 3 (below) shows a more in-depth breakdown of the planted stock survival and the likely cause of death. Jack pine in particular was heavily browsed over the other two species.
Figure 6: Planted stock survival by species and type of site preparation (harrow vs no action) five years after planting. Additional treatments included annual bud capping and individual tree release at year 4.
Table 2. Planted species survival based on site preparation treatments.
| Species (treatment) | Survival | Mortality |
| Jack Pine (harrow) | 53% | 47% |
| Jack Pine (no site prep) | 27% | 74% |
| White Pine (harrow) | 73% | 27% |
| White Pine (no site prep) | 73% | 27% |
| White Spruce (harrow) | 60% | 40% |
| White Spruce (no site prep) | 73% | 27% |
The Northern Research Station also followed planted stock growth on the same 30 trees of each species over five years. Table 3 shows diameter and height growth of white pine to be significantly greater in the harrowed portion of the stand compared to the no prep. Jack pine and white spruce diameter and height growth vary between the harrow and no action treatment.
Table 3. Diameter and height response of the three planted species five years post-planting based on site preparation.
| Species | Harrow | No Prep |
| 5 Year Height | ||
| Jack Pine | 28.7 cm | 29.6 cm |
| White Pine | 79.6 cm | 48.8 cm |
| White Spruce | 61.6 cm | 69.4 cm |
| 5 Year Diameter | ||
| Jack Pine | 3.7 mm | 3.4 mm |
| White Pine | 8.3 mm | 5.5 mm |
| White Spruce | 8.1 mm | 10.0 mm |
Figure 7: A post-harvest reserve is seen on the right.
Figure 8 : CNF variable retention red pine treatment during an April 2018 tour showing an unharvested patch at right.
Plans for future treatments
The Northern Research Station has scheduled vegetation monitoring of residual tree growth and survival (in research plots) every five years. Survival and growth of planted stock and all other woody species will be conducted annually for the first 5 years then periodically every 2-5 years thereafter.
No other future vegetation treatments are planned at this time but could be considered as vegetation monitoring continues.
Costs and economic considerations
This project was funded by the Northern Research Station and timber proceeds covered post-harvest treatments including; site prep, planted stock and planting, individual tree release, and bud-capping.
Other notes
This case study was developed with support from the United States Department of Agriculture's National Institute for Food and Agriculture (USDA-NIFA), Renewable Resources Extension Act (RREA). Project #MIN-44-E02, principal investigator Eli Sagor, University of Minnesota.
Summary / lessons learned / additional thoughts
Some things that were considered for future variable retention harvest for this forest type could be to plant climate change adapted oak species such as bur oak or white oak to provide options for a higher commercial value product. It also could have been beneficial to vary the residuals in the matrix spatially to promote increased growth and survival of the intolerant species to favor jack pine and red pine. Summer harvest would have been preferred for increased scarification. Site prep was effective at reducing hazel and favored increased seedling growth for white pine. During individual tree release oak stump sprouts could have been reduced to one or two good form individuals to encourage good formed bole and increase growth. Overall, the goals to increase growth of residuals, promote multi-cohort development, reserve unique biological legacies, and create more complex structure were achieved.